MIOCENE MOLLUSCA AND OliUSTACEA. ■ 55 



serve<I in the Academy of Natural Sci^ences at Philadelphia. The specimen 

 is considerably waterworn, so that the teeth and the marginal crenulations 

 are worn away, but the exterior markings of the shell are still plainly 

 visible, leaving no douiit of the specific identity. 



ASTARTE THOMASI. 



Plate VIII, Figs. 3-7. 



Antartc Thomasi Counitl; Proc. Acad. Nat. Sei., Phil., 1855, i). 2G7; Am. Jour. Coucli., 

 vol. 2, p. 73, PI. IV, Fifj;-. 10; Proc. Acad. Nat. Sci. Pliil., 18(J2, p. 578; Meek, 

 (Jbeck List Miocene Foss., p. 7; lleilpriii, Coiit. Tert. Geol. and Pal. U. S., p. 8; 

 Proc. Acad. Nar. Sci., 1887, pp. 400. and 402. 



? Astarte exaltata Heilprin; Gout. Tert. Creol. and Palaeont. U. S., p. 8. 



"Triangular, not ventricose, inequilateral; ribs concentric, robust, 

 recurved; conoeutric lines more or less marked, minute; toward the poste- 

 rior ends the ribs suddenly become obsolete; extremity truncated, nearly 

 direct, or sloping iuwards ; iuner margin crenulated; lunula large, ovate, 

 acute, deeply excavated." (Conrad in Proc. Acad. Nat. Sci. Phil., vol. 7, 

 p. 267.) 



This species somewhat closelv resemliles the recent Asfarte castanea of 

 our own coast, but is souiewhat smaller generally, and less arcuate. The 

 shell is ovatelv triang'ular, longer than high, and moderately convex ; the 

 beaks prominent pointed and well directed forward. The concentric ribs, 

 15 to 20 in number, are rounded on the surface or slightly arched back- 

 wards, and are concentricallv striate on their surfaces. The lumile is deep, 

 elongate-ovate in form, and pointed below; the escutcheon is deep and nar- 

 rowlv lanceolate in form, lx)th being somewhat variable in different indi- 

 vi(Uials. -The sul)stance of the shell is thick and heavy, and the muscular 

 in^jrints in the intcn-ior are large and strongly marked. Hinge })late small 

 and narrow, crenulations of the inner l)order rather coarse and deeply 

 marked. 



The species is most nearlv allied to A. <:iiilf((ta (Jon. (Medial Tert., p. 

 6G, PI. XXXVII, Fig. (!) of any fossil form of the Miocene deposits, l)ut it is 

 more triangular, less rounded on the base, and not so dee|)lv arcuate ante- 

 rior to the beak. The surface structure, however, is quite distinct; that one 



